Various synthetic and naturally occurring water-soluble polymers have been developed which exhibit excellent thickening and flocculating properties. These polymers are well known to the the art and have been described in numerous publications and patents. Most commonly used are acrylamide polymers which include polyacrylamide and its water-soluble copolymeric derivatives such as acrylamide-acrylic acid and acrylamide-acrylic acid salt which contains 95-5 percent by weight acrylamide. Copolymers of acrylamide with vinyl monomeric such as maleic anhydride, acrylonitrile, styrene and the like are also useful. Other useful water-soluble vinyl polymers are described in detail in U.S. Pat. Nos. 3,418,237; 3,259,570 and 3,171,805. The polymers are generally available in powder form but useful only when dissolved in water.
One method of use has been to first disperse the polymer in a carrier such as oil. The polymer is generally highly concentrated in the carrier and must be diluted to a concentration of approximately 8%-10% in water or other diluents before use. One method using an oil based carrier is disclosed in U.S. Pat. No. 3,624,019.
The polymers have molecular weights of up to 25,000,000. As such, they exist in the carrier in tight coils. The active sites for treatment of wastes are believed to be along the chain and in the coil form the polymers are not effective. In addition to being diluted, the polymers must also be allowed to uncoil to expose the active sites and activate the polymer.
Due to the size and length of these polymers, they must be mixed gently to prevent breaking up of the chains into smaller, less efficient particles. There is therefore, presented a problem in the mixing and dispersion of polymer in diluent. If the polymer becomes uncoiled during mixing, it can be broken up. Methods and apparatus have been designed to disperse the polymer gently in water--see for example, U.S. Pat. No. 4,522,502 where the inventor has gone to great lengths to design a mixing apparatus that will not break up the polymer during dilution and activation.
The apparatus as described in U.S. Pat. No. 4,522,502 has several drawbacks. One major problem as disclosed is that the combination impeller and nozzle arrangement causes vortexing in the mixing tank which prevents effective mixing. In particular, the placement of the nozzle closely adjacent to the impeller contributes to this problem. The addition of the mixing vanes helps to alleviate the problem but increases the shear forces on the polymer molecules which increase the possibility of break-up of the molecules. This problem would be overcome if the polymer did not age in the mixing chamber.
Other methods and apparatus for diluting polymer are disclosed in U.S. Pat. Nos. 4,217,145; 3,807,701; 4,218,147; 4,233,265; 4,125,574; 4,057,223; 3,186,803; 3,434,804 and 3,765,655. None of the above referenced patents disclose a particularly designed aging tank to allow the polymer to become activated after dilution.